The present invention relates to a sensing device for detecting various kinds of physical quantities, and more particularly to a sensing device having a function for adjusting output characteristics of the sensing device or a control state of a sensing element.
A known way of adjusting output characteristics of an acceleration sensing device by applying an electric signal to an adjusting terminal is disclosed in Japanese Patent Application Laid-Open No. 5-340958. The acceleration sensor has an acceleration detection processing circuit provided with a sensitivity adjusting unit and a zero-point adjusting unit, and an adjusting unit capable of varying a basic output characteristic of sensitivity. The adjusting unit is constructed of a plurality of resistors and switches, and on-off operation of the switch is performed by external on-chip trimming.
In the prior art described above, the adjusting terminals capable of performing on-off operation of the adjusting switches are provided on an electronic circuit board, and in a fabrication process of the product there are a filling process of a gel into a housing having the circuit board inside after adjusting the output characteristic and heating processes for bonding a cover and setting the gel and the cover adhesive. Variations of output characteristics in the final products are caused by variations of output characteristics caused by the process.
Further, in an air flow measuring instrument for an internal combustion engine, in order to make it small in size, light in weight and low in cost, it is preferable that an air flow sensing unit is integrated in a housing containing a circuit board inside, and the housing is inserted and mounted so that the sensing device is positioned in an air intake flow passage of the internal combustion engine. Since the adjusting work needs to be performed by actually flowing air through the flow sensing unit, the air flow measuring instrument is mounted on a rig corresponding to the air intake flow passage after almost completing the housing and the flow sensing unit, and adjusting work is performed from the outside of the rig by actually flowing air. Apparatus capable of performing such adjusting work is necessary.
Particularly, in a thermal type air flow measuring instrument, the sensing element can be made small in size and the sensing element needs to be electrically connected to an electronic circuit for controlling the sensing element and outputting. Therefore, it is possible to provide a small-sized and low-cost air flow measuring instrument in which a flow sensing unit is integrated in a housing containing an electronic circuit. However, since the electronic circuit is also placed in the air intake flow passage, adjusting work is performed from the outside of the air intake flow passage when the adjusting work is performed by actually flowing air through the flow sensing unit. Here again, apparatus capable of performing such adjusting work is necessary. Further, in a case where the sensing element is placed in an auxiliary passage from the viewpoint of various kinds of performance and reliability, in taking it into consideration making the instrument small in size and low in cost, the number of parts is reduced by forming the auxiliary passage in the housing and forming the auxiliary passage by the cover of the housing. However, in taking into consideration the effect of variations in shapes of the auxiliary passage on the output characteristics, it is necessary to perform adjustment by actually flowing air after completion of the auxiliary passage, and apparatus capable of adjusting from external is further required.
An object of the present invention is to provide a highly accurate sensing device, the characteristic adjustment of which can be performed in a final, i.e. the last, process step.
Another object of the present invention is to provide a low-cost sensing device in which the sensing elements and the electronic circuit are integrated to reduce the number of parts, the size and the weight, and it is possible to easily perform the characteristic adjustment of the sensing device.
Another object of the present invention is to provide a sensing device, which is suitable for the environment of actual use, and in which the characteristic adjustment can be performed under a state that the sensing device is set in the environment of actual use.
In the present invention, for example, adjustment of output characteristic can be performed in the final process in production of the devices as products, and occurrence of the variations of the products due to change in the output characteristic in such processes as filling the gel and bonding the cover is suppressed.
In order to solve the above-mentioned problems and to achieve the above objects, in addition to the electric power supply, ground and output terminals which are provided in a common sensing device, an output characteristic adjusting terminal of the sensing device or a control quantity adjusting terminal of a sensing element is provided outside a housing for containing an electronic circuit inside.
Further, in order to prevent problems such as corrosion of the terminals or short-circuit caused by coming in contact with a conductive material under the environment of actual use of the sensing device, the adjusting terminal is covered with adhesive or the like, or the adjusting terminal is arranged inside a connector housing containing the electric power supply, ground and output terminals so that foreign objects are prevented from coming in contacting with the terminals and the connector housing becomes a water-proof place under the environment of actual use in which the associating connector is connected. In that case, by arranging the adjusting terminal at a lower (deeper) level to the depth direction of the connector housing than the level of the power source terminal etc., it is possible to prevent the power source terminal etc. from coming in contact with another thing, for example, contact with a probe during adjusting work or contact with an associating connector when the associating connector is connected. Further, by arranging the adjusting terminal in a hole provided on the bottom of the connector housing, it is possible to prevent electrical short-circuit during adjusting work with more certainty.